Setting up local DNS server for subdomain of existing domain for iPhone

Question

Problem description

I am developing a web application with a React Frontend and PHP backend. For crossorigin and cookie Reasons I need to host the frontend on the same domain namespace as the backend. I need to access a deployed version of my backend with my local computer which hosts the fronend.

Previous solution

(Working only locally not on devices on the network)

For my Mac, I got it working reliably like this:

hosts

...
127.0.0.1   local.mydomain.com
::1         local.mydomain.com
...

New Solution

(not yet working as expected)

I implemented a DNS server on my Synology (disabled my Macs host entries) and set it up in my local network router like this:

Name	Type	TTL	Information
.local.mydomain.com	NS	86400	ns.local.mydomain.com.
ns.local.mydomain.com	A	86400	192.168.0.10 (local fixed IP of my computer)
anothersub.local.mydomain.com	A	86400	192.168.0.10 (local fixed IP of my computer)

I also would like to instead of anothersub.local.mydomain.com use *.local.mydomain.com, however, when I did so, it always added a www to the local.mydomain.com on my iPhone like www.local.mydomain.com which does prevent my app from working properly. On my Mac on the other hand, it works as expected. (Update: It is not, I forgot to disable some hosts entries)

I am not sure if it is some iPhone behavior but it seems like the iPhone always calls both local.mydomain.com and www.local.mydomain.com whenever I enter local.mydomain.com. Generally my iPhone can access my app on my computer also on www.local.mydomain.com, but it just doesn't work as expected.

mydomain.com is a registered domain on the web, while I haven't registered the local.mydomain.com subdomain on my webserver. I suspect, however, if my iPhone calls www.local.mydomain.com it will somehow land on my webserver and not my local dns, getting an answer but of course not a success.

Is there any entry I can add to my DNS list to forward any call to www.local.mydomain.com to local.mydomain.com?

Updated question: how do I get local.mydomain.com and not only anothersub.local.mydomain.com working?

Answer 1

So I found out I only had a NS entry but no A entry for my root subdomain. In order to get it work I needed to add an entry like this

Name	Type	TTL	Information
local.mydomain.com	A	86400	192.168.0.10 (local IP of my computer)

However, I also want to point out that it is required to disable DNS Rebind Protection in the Router and iCloud Private Relay on your devices in order to work.

The reason why it was working for www.local.mydomain.com was because I already had an entry like this before which I removed but I suppose was still cached on my device:

Name	Type	TTL	Information
*.local.mydomain.com	A	86400	192.168.0.10 (local IP of my computer)

So my device tried both with and without the www and with the www it had a success so it appended it.

Setup on Webserver

So I also finally managed to move my DNS setup to my webserver. This way I do not need to disable iCloud Private Relay. My setup looks like this. (I needed to wait for a while before it was synced to my DNS and worked)

Name	Type	TTL	Information
local.mydomain.com	A	86400	192.168.0.10 (local IP of my computer)
anothersub.local.mydomain.com	A	86400	192.168.0.10 (local IP of my computer)

I might possibly manage to replace anothersub.local.mydomain.com with *.local.mydomain.com for wildcard subdomains but it is not really required for my use case.